Data compression systems reduce the number of bits needed to transmit and store a digital information signal. As a result, a lower bandwidth communication channel can be employed to transmit a compressed video signal in comparison to an uncompressed video signal. Similarly, a similar, reduced capacity storage device, which can comprise a memory or a magnetic storage medium, can be used for storing the compressed video signal. A general information signal compression system includes an encoder, which converts the video signal into a compressed signal, and a decoder, which reconstructs the video signal based upon the compressed signal.
In the design of a video compression system, an objective is to reduce the number of bits needed to represent the video signal while preserving its information content. Previous methods and systems for video compression have achieved a reasonable quality of content preservation at transmission bit rates of 40 to 60 to 1 less than the original. These methods and systems are based upon directly compressing a waveform representation of the video signal. An alternative compression format utilizes a limited collection of predetermined library objects that symbolically represent waveform portions in a reduced amount of bits. However, the previously known compression formats are accessible only in response to receipt of an appropriate signal. Moreover, symbolic compression has been limited to generic objects and does not fully compress the details of a particular aural or visual signal content.